Database backup copies

When IMS takes a regular system checkpoint, it records internal control information for DL/I (for Fast Path, IMS also records buffers and MSDBs), but it does not record the external contents of the database. If the database is lost, examining the last system checkpoint does not help. The log can tell you what changes have occurred, but without a backup copy of the database, recovery is impossible.

Recommendation: Make a backup copy of the database after you initially load it, and make new backup copies at regular intervals. The more recent the backup copy is, the fewer log change records need to be processed during recovery, thus reducing the time that is needed for recovery.

IMS enables you to make backup copies in these ways:

The Database Image Copy utility (DFSUDMP0) runs offline and uses access method services to make the copy.
The Database Image Copy 2 utility (DFSUDMT0) runs offline and invokes either DFSMSdss Concurrent Copy or DFSMSdss fast replication to make the copy.
The Online Database Image Copy utility (DFSUICP0) runs online and uses IMS services to make the copy.
The unloaded data that is output from the HISAM Reorganization Unload utility (DFSURUL0) can be used as a backup copy.
HSSP processing can also create image copies of DEDB areas.

When these utilities run, they can (depending on installation parameters) call DBRC to update essential information in the RECON data set. If you use a supported image copy utility, DBRC records the image copies for registered databases. DBRC also generates the JCL for the utility if you enter the GENJCL.IC or GENJCL.OIC command.

You can also use various utilities supplied by the operating system to make your backup copies; however, these do not interact with DBRC, and so you need to take certain actions to notify DBRC of your non-standard image copies.

Related reading: See IMS Version 15.2 Database Administration for more information on HSSP processing of DEDB areas.